Step 1

Heat olive oil in a large saucepan or saucier over medium heat until shimmering. Add leek and celery. Season with salt and cook, stirring, until vegetables are softened but not browned, about 5 minutes. If pan starts to look dry at any point, add a small splash of olive oil. Add garlic and cook, stirring, until fragrant, about 30 seconds. Add zucchini and cook, stirring, for 1 minute. Add half of basil, stir to combine, and add water.

Step 2

Bring to a simmer and cook, stirring occasionally, until zucchini is tender but still bright green, about 10 minutes. Add remaining half of basil and blend soup using a handheld immersion blender or a countertop blender until it is as rough or as smooth as you like it. Season to taste with salt, black pepper, and lemon juice and serve, drizzling with additional olive oil at the table.